This invention relates to admixtures for incorporation into hydraulic cement mixes which are nonplastic by virtue of low water contents per unit volume, such as those used in making masonry units, pipe and the like. Examples are concrete block, concrete pipe and other concrete products and structures. Such nonplastic mixes contain portland cement, optionally pozzolanic additions, aggregate and water, yet they differ significantly from conventional highly-workable plastic mixes, which contain relatively much greater proportions of water, and normally set and harden under ambient conditions. In contrast, nonplastic mixes are mechanically forced into molds and set and harden under the influence of steam and elevated temperatures. Because of these differences, the problems encountered with the two types of cementitious mixes differ significantly.
Thus, admixtures developed for use in plastic cementitious mixes are often unsuitable for use in nonplastic mixes, and vice versa. For example, the water-reducing and plasticizing agents employed with plastic mixes may not be applicable to nonplastic mixes, and admixtures which perform in plastic mixes as air-entraining agents do not act in this manner in nonplastic mixes. Conversely, admixtures suitable for use in nonplastic mixes may have adverse effects, for example with respect to air entrainment, in plastic mixes.